Solid state image sensors, also known as imagers, have commonly been used in photo-imaging applications. An imager absorbs incident radiation of a particular wavelength (such as optical photons, x-rays, or the like) and generates an electrical signal corresponding to the absorbed radiation. There are a number of different types of semiconductor-based imagers, including charge coupled devices (CCDs), photodiode arrays, charge injection devices (CIDs), hybrid focal plan arrays, and complementary metal oxide semiconductor (CMOS) imagers. These imagers, when used with appropriate imaging circuits, capture, process and display images for various purposes. Current applications of solid state imagers include cameras, scanners, machine vision systems, vehicle navigation systems, video telephones, computer input devices, surveillance systems, auto focus systems, star trackers, motion detector systems, and image stabilization systems among other uses.
For capture of visible or infrared images these imagers typically consist of an array of pixel cells containing photosensors, where each pixel cell produces a signal corresponding to the intensity of light impinging on that element when an image is focused on the array. These signals may then be stored, for example, to display a corresponding image on a monitor or otherwise used to provide information about the optical image. The photosensors are typically phototransistors, photoconductors or photodiodes. The magnitude of the signal produced by each pixel, therefore, is proportional to the amount of light impinging on the photosensor.
To allow the photosensors to capture a color image within the visual image, the photosensors are often formed to separately detect red (R) photons, green (G) photons and blue (B) photons. Accordingly, each pixel is formed to be sensitive only to one color or spectral band. For this, a color filter array (CFA) is typically placed in front of the array of pixels so that each pixel measures the light of the color of its associated filter. Thus, each pixel of a color image sensor is covered with either a red, green or blue filter, according to a specific pattern.
Color filter arrays are commonly arranged in a mosaic sequential pattern of red, green, and blue filters, such as a Bayer filter pattern, which is quartet-ordered with successive rows that alternate red and green filters, then green and blue filters. To form the color filters, a resist is typically used containing a color pigment. For example, the Bayer filter pattern requires the printing and patterning of three resist layers on a passivation layer, each of a respective color. The individual color filters are formed to be adjacent one another in the completed color filter array.
The photoresist commonly used to form the color filters has limited resolution, and may suffer from shrinkage and poor planarity which may affect the optical properties of the color filter array as well as an overlying lens array. In addition, when the color filters are formed in close proximity or in contact with one another, stray light can travel between pixels resulting in optical crosstalk.
Accordingly, it is advantageous to provide an improved structure for the color filter array which more effectively and accurately defines the boundaries and colors of the various color filters to improve color separation and/or which blocks light from being transmitted between color filters to reduce optical crosstalk with a minimum of added complexity to the manufacturing process and/or increase in fabrication costs. It is also advantageous to provide a method of fabricating a color filter array exhibiting these improvements.